cache generates extra Content-type header

The cache system appears to generate an extra Content-type header as part of the content when enabled.

Here are the headers without cache enabled (from Rex Swain's HTTP viewer http://www.rexswain.com/httpview.html):

HTTP/1.1·200·OK(CR)
(LF)
Date:·Fri,·06·Feb·2004·05:26:01·GMT(CR)
(LF)
Server:·Apache/1.3.29·(Unix)(CR)
(LF)
Cache-Control:·no-store,·no-cache,·must-revalidate,·post-check=0,·pre- check=0(CR)
(LF)
Expires:·Thu,·19·Nov·1981·08:52:00·GMT(CR)
(LF)
Pragma:·no-cache(CR)
(LF)
X-Powered-By:·PHP/4.2.3(CR)
(LF)
Set-Cookie:·PHPSESSID=4fabbfb6a476644943ca2681b80ba47d;·path=/(CR)
(LF)
Connection:·close(CR)
(LF)
Content-Type:·text/html;·charset=utf-8(CR)
(LF)
(CR)
(LF)

Here is the same page, with the cache enabled:

HTTP/1.1·200·OK(CR)
(LF)
Date:·Fri,·06·Feb·2004·05:24:57·GMT(CR)
(LF)
Server:·Apache/1.3.29·(Unix)(CR)
(LF)
Cache-Control:·no-store,·no-cache,·must-revalidate,·post-check=0,·pre- check=0(CR)
(LF)
ETag:·"e13d6fd8153a8acd4ee8c532415fd107"(CR)
(LF)
Expires:·Thu,·19·Nov·1981·08:52:00·GMT(CR)
(LF)
Pragma:·no-cache(CR)
(LF)
X-Powered-By:·PHP/4.2.3(CR)
(LF)
Set-Cookie:·PHPSESSID=a5f8deffd48bc7065a540409f24aff9b;·path=/(CR)
(LF)
Last-Modified:·Fri,·06·Feb·2004·05:23:48·GMT(CR)
(LF)
Connection:·close(CR)
(LF)
Content-Type:·text/plain(CR)
(LF)
(CR)
(LF)
Content-type:·text/html(CR)
(LF)
(CR)
(LF)

Note the extra 27 characters "Content-type: text/html(CR)(LF)".

This causes Mozilla and Netscape browsers to fail to display HTML, displaying instead the text source. MSIE 6 displays the extra header as text and then renders the HTML.